Atrial natriuretic factor (ANF) is involved in controlling blood pressure and salt balance. The factors which regulate the expression of the ANF gene will be studied. Rats will be treated with agents that are known to affect blood pressure and extracellular fluid volume, e.g., high salt diet, converting enzyme inhibitors and beta-blockers. Following treatment, the atria will be removed and levels of ANF mRNA will be analyzed by hybridization. Also, the steroid control of ANF gene expression will be studied in a similar way in the intact rat and after transfer of the cloned human ANF gene to steroid responsive tissue culture cells. Finally, the levels of ANF mRNA in two animal models for human disease will be studied. These are the spontaneously hypertensive rat and the cardiomyopathic hamster. This research should provide information on the factors which regulate the ANF gene and should show how the ANF system interacts with the renin-angiotensin system. This will be helpful in evaluating the use of ANF as a therapeutic agent for lowering blood pressre, or as a diuretic, and will provide the basis for a more extensive phase II study of the applications of ANF.